I read an article the other day which claimed that lavender is immune to disease, a quality that is linked to its healing properties. I'm the first to hop in a bath infused with lavender when I need a break and I am certain that the relaxation it gives me is good for my mental health if nothing else. I also know that many people benefit from using it in other ways, but I feel moved to set the record straight. In the everyday running of our nursery, we are always on the lookout for signs of disease on our plants. They are packed in pretty tight and one rotten apple, so to speak, could easily cause us to lose a lot of stock.
Now, it is true that I have never seen any of the two diseases described below on our lavender or anyone else's, so I am certain that it is a very disease resistant plant and I am not trying to warn the world of impending lavender catastrophe. Nevertheless, you may come across these invaders in your travels and even
prevent disaster by raising the alarm. Here are the things that we check on to be sure that our plants are healthy:
Alfa Mosaic Virus: This one is quite easy to spot. The leaves will begin to turn yellow in patches and then curl up into contorted shapes. This virus can be spread by both insects and your hands, so it is important to whip out infected plants quickly, using something disposable like a sheet of newspaper to hold the plant. As with any diseased plant material, the best thing to do is burn it. If you really have nowhere to make a fire, bag them up tightly and put them in the bin.
Lavender Shab Disease - Phomopsis lavandula: This is a fungus that kills the stems of the lavender. The clearest sign of it is when all the shoots wilt suddenly, even though there has been no drought. There was a lavender shab epidemic about 40 years ago that killed vast amounts of commercially grown lavender (where the wind could easily spread fungal spores along the rows of plants) and although it seems to have since disappeared, anyone who grows, sells or maintains large amounts of lavender is on the lookout for this microscopic killer. Close inspection of the affected plants (you may need a magnifying glass) will reveal very small black shapes called pycnidia emerging from the bark. If you saw them under a powerful microscope, you would see that they are cup shaped and full of spores. Again, do your best to try and burn the affected plants.
Wet Feet: This isn't a disease but it spells a far greater hazard for lavender plants than the other two put together. This is the thing that we check every lavender plant for before it gets sent to its new home. If the soil around lavender's roots is too wet, especially over winter, rot sets in and the bark begins to die. It will be easy to pull the bark away from the base of the main stem and the stem itself may simply twist off from the roots with very little force. Larger plants can struggle on for a little while like this but really they are dead already (and just haven't realised it).
The chances of coming across Shab or Alfa Mosaic Virus are pretty slim and my bet is that you will never have a problem with them. But if you have any lavender woes, please let us know and we'd be happy to give our opinion. Anyway start with healthy stock, like our lavender plants, ideally planted in April or early May and you should be fine.
Relax, enjoy and watch your garden grow!